| China’s total ban on imports of waste plastics has become a certainty along with the reform of imported solid waste management system,as plastic products processing raw materials imported recycled plastic pellets become an important supply of raw materials for plastic products in China.Research on the physical properties of imported recycled plastic pellets and the characteristics of pollutants is particularly important for the improvement of quality standards of imported recycled plastic pellets.At present,there are more studies on pollutants in plastic products,but there are few studies on imported recycled plastic pellets.In order to reduce the probability of environmental risks caused by imported plastic products,this thesis takes imported recycled plastic pellets as the research object,screens the characteristic pollutants in the pellets and their own physical properties and analyzes the content characteristics,clarifies the characteristic pollutant content,pollutant characteristics and migration characteristics in the recycled plastic pellets and conducts simulation studies in the laboratory,analyzes the main factors affecting the physical properties,and provides reasonable data support for improving the quality standard of imported recycled plastic pellets in terms of pollutant The study will provide reasonable data support to improve the quality standards of imported recycled plastic pellets.(1)The physical properties and characteristic pollutant content of imported recycled plastic pellets were characterized.According to literature research and pre-experiments,the main physical properties of imported recycled plastic pellets are water content,ash content and density,and the characteristic pollutants are mainly heavy metals(Ba,Zn,Pb,Sb)and volatile organic compounds(VOCs).The highest content of heavy metal Sb was found in PET-type pellets,ranging from 63.51 to 182.90 mg/kg for each type.These heavy metals mainly come from recycled materials and additives.5 types of imported recycled plastic pellets can volatilize 4-12 kinds of VOCs,among which the main kind of VOC is1,2,4-trimethylbenzene,with the highest content of each kind being 384.66μg/m3 for PE-2,76.18μg/m~3for PP-10,291.33μg/m~3for PET-2,and 291.33μg/m3 for PS-3g/m~3,62.86μg/m~3for PS-3,and 260.70μg/m~3for ABS-2.(2)The effect of cleaning conditions on the content of characteristic contaminants of imported recycled plastic pellets.The total content of heavy metals in the cleaning solution of primary,secondary and tertiary cleaning were 901.32μg/kg,426.87,380.09μg/kg,respectively.the total content of heavy metals in the cleaning solution of ultrasonic cleaning and wet cleaning were 1047.18μg/kg,763.84μg/kg,respectively.the content of cleaning solution in alkaline water cleaning and normal water cleaning were 930.49,763.84 In 5℃,20℃,35℃,50℃is the total content of heavy metals in the cleaning solution 914.68,966.07,1052.24,386.13μg/kg.in summary,the best cleaning conditions can be selected often 20℃～35℃using wet alkaline water cleaning,cleaning times for two.(3)The physical properties and characteristic pollutant content of washed waste plastics were analyzed.10 kinds of waste plastics were detected with more heavy metals than imported recycled plastic pellets,mainly As,Zn,Ba,Sb,Cr,Ni,and the highest heavy metal As content in waste plastics,between 30 and 400 mg/kg,among which waste gasoline drums,waste chemical drums and waste ink bottles had higher heavy metal content than other 7kinds of waste plastics.10 kinds of waste plastics were detected with less or no contaminants,such as PET bottles,which had 2-4 VOCs.The physical properties of the 10 waste plastics are similar to those of the other 7 waste plastics,except for the slightly different waste gasoline drums,chemical drums and ink bottles,which contain contaminants.The physical properties of the 10 waste plastics were similar to those of imported recycled plastic pellets.(4)Correlation analysis of pollutants,physical properties and recycled pellets of waste plastics.10 kinds of waste plastics and 5 types of imported recycled plastic particles correspond to each other.Pollution characteristics are similar to waste plastics,imported recycled plastic particles physical properties,characteristic pollutants and recommended uses to infer that imported recycled particles from a certain waste plastic,and characteristic pollutant sources,migration and physical influencing factors can also be inferred from these to determine.According to the above research results to provide imported recycled plastic pellets and characteristic pollutant traceability analysis data,while providing imported recycled plastic pellets with heavy metals,VOCs,water content,density,ash to provide control index data,strict control of import standards to reduce the migration of pollutants at source,in order to obtain higher quality plastic products raw materials,namely imported recycled plastic pellets. |
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